In view of the high cost of fossil fuel there has lately been great activity in the development of wind motors for generation of power, and many designs of runners have become available. Use of wind power is not new, in fact, windmills were used hundreds of years ago for milling corn or for raising water, their impellers usually consisting of radial struts to which sails or wooden lath construction are attached. This type of wind motor was replaced, in the last century by multi-vane runners which comprise a plurality of radial, inclined vanes fastened between an outer and an inner ring, the latter ring being mounted on a horizontal or slightly inclined shaft. The multi-vane runner has lately been further developed, resulting in a rotor wherein all elements work under stress, this embodiment being known as the CHALK TURBINE. Herein hollow vanes are radially positioned between two concentric rings, with tension wires stretched inside the vanes and connecting the two rings under tension. In spite of their other advantages, multi-vane impellers show a relatively low aerodynamic efficiency and are, therefore, used for only relatively small outputs.
The windmill-type runner, on the other hand, has given way to a rotor provided with two to six aerodynamically shaped, generally hollow, blades which are being built to considerable diameters and large output at high efficiency, and which form one of the main points of today's development.
The main drawback of the existing windmotors is their stiff and rigid construction which makes them liable to damage at high wind velocities, and requires special means for turning them out of the wind direction during storms and heavy squalls, in order to prevent breakdown of the installation. These precautionary measures comprise either means for turning the turbine shaft perpendicular to the wind direction as soon as the wind reaches a dangerous speed, or means for altering the inclination of each individual blade in accordance with wind velocity. Another drawback of the rigid construction is the increase in weight with increasing diameter of the rotor which limits the wind motor capacity on the one hand, and makes requirement for very strong support structures, on the other; both result in high specific cost per kw produced.
It is, therefore, the main object of the invention to provide a rotor or impeller of light weight which lends itself to be built to very large diameters. It is another object to provide a resilient and flexible impeller, thus preventing any danger of damage by high wind velocities, and it is still another object to provide such impeller with built-in, integral braking means so as to limit its revolutions to a safe margin of stress of the material.
A further object, actually resulting from the previous demands, is to permit the installation of such light-weight at great heights, so as to utilize the higher wind velocities occurring in these zones.